If the drives are as old as the rest of the hardware, then they are well past the average life expectancy of a HD. Try 1 at a time and see if the machine will recognize at least 1 drive. Its unlikely both died at the same time but, one might be dead.

That two drives cannot be detected at the same time, both before when I had the same problem, and now, eliminates the chance that of that.

And, the 2 drives failed to be detected once before, both at the same time, and then were both detected at the same time when I was able to get them to be detected again. The previous time I did nothing but restart the computer several times. Nothing else was checked or done.

u did not give us any motherboard information nor the SATA or PATA HDD types?the cables ur connecting the HDD to motherboard might be damaged or faulty cables, are they detected in bios always? did u try them on another computer?

"Desktop, Pentium 3-500, 384mg memory" You are obviously not running Vista on this rig. On a board that old the drives are certainly not SATA but IDE ( PATA) I presume you have both hanging off the one IDE cable and your optic drive is on the other. There is a simple way to test if the motherboard has a problem.Switch the IDE cables in the motherboard connectors so the optic drive is connected where the hard drives were and vice-versa. Now try to boot up. If the hard drives are now detected but the optic is missing your motherboard IDE controller is shot.

OK. The motherboard controller is OK so you now have either a faulty IDE cable or faulty drive. Try one drive at a time and try using the cable the optic drives are currently attached to. Let us know what happens.

Check the jumper settings, often them manufacturers use the 'cable select' option for the jumpers, but you may have less trouble if you reset one to 'Master' and the other to 'Slave'. Also note that if you have the older 40 pin/ 40 Wire cable type, you may have less trouble and better speed on the newer drives if you make sure you have the relatively newer 40 pin/ 80 Wire cable type which supports the higher speed of the newer IDE drives. (the visual difference is the older one has all connectors the same color, the newer has three different color connectors, Google for an image to see the difference)

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